From: "Leo A. Martin" leo at possi.org> on 2005.12.18 at 23:07:05(13626)Actually, Astrophytum and most other cacti can be grown in almost
anything, including pure peat moss. Most large-scale commercial nurseries
who raise seedlings use a mostly-peat mix and water (and fertilize) almost
every day.

The question is - what are your cultural practices? Most hobbyists don't
do well with peat-based cactus mixes, since once peat dries, it is very
hard to rewet.

Using peat or coir, cacti usually need to be repotted every 2-3 years,
since the medium breaks down.

Rather than focusing on what kind of stuff, how often, and how much, it is
better to think about

- How wet do I want it to be most of the time?
- How much plant-care time do I have, and at what intervals can I look at
my plants?
- How often am I willing to repot my plants?

Once you can answer these questions, you are ready to experiment with
potting mixes. Start with one mix. Fill a pot like the ones you wish to
use with the mix. Get the pot wet. Set the pot in your typical growing
area.

Now poke a moisture meter into the pot every day until the moisture meter
says it's dry.

Remember that or, better yet, write it down.

Now go on to the next mix.

Select a mix and pot based on how long you want the pot to stay moist. For
cacti, you want the pot and soil combination to stay moist for 7-10 days
after a watering during the growing season.

If this all seems too much trouble, I suggest you go watch television and
eat.